The psoas abscess is very uncommon during pregnancy. If the abscess is secondary, surgical intervention on the predisposing disease is necessary for better outcome. We report the first case of a psoas abscess complicating Crohn's disease during ongoing pregnancy. A 28-year-old gravid woman with a history of ileal Crohn's disease presented at 16 weeks of gestation with high fever, right lower quadrant and low back pain. A diagnosis of right multilocular psoas abscess was made by MRI. Due to the impossibility of drainage and surgical intervention, she was treated by administration of appropriate antibiotics and total parenteral nutrition. The patient transvaginally delivered a female baby at the 40th gestational week without complications. Medical treatment of psoas abscess seems to be a choice in selected cases, although it requires a long hospital stay and continued careful observation due to further risk of infections such as catheter related blood stream infections.